Total online sales for September grew 8% from a year earlier, according to retail research group IMRG Capgemini.

Online sales were £3.9bn, up 1.9% from August, which was an "unusually low rate", the report said.

Clothes and electrical retailers suffered most as the recession continued to take its toll, it added.

However the report forecast that sales growth would pick up again to year-on-year levels of about 15%.

"The underlying trend is still that customers are turning to the internet to make more informed purchase decisions," said Mike Petevinos, head of consulting for retail at Capgemini UK.

An upturn in High Street sales had been expected, as many retailers began their promotional activity for winter early this year, he added.

And above average temperatures and more sunshine in September may have led online shoppers to "abandon their computer screens in favour of the High Street" the report suggested.

Other alternatives

Postal workers have threatened a series of strikes on top of rolling industrial action, which as been on-going in some areas for month.

These "may have acted as a deterrent for online shoppers" the report said, adding it "will continue to be a key concern for e-retailers in the lead up to Christmas."

John Lewis has already announced that it is working with other carriers in order to avoid disruption to its online deliveries from any Royal Mail strike, while Amazon has said it is taking similar action.

However, smaller businesses - especially those sending low value items - have said that prohibitive costs have meant that using other delivery services is not viable.

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